3M 4200 Fast Cure: Fixing a Jon Boat Transom

The transom plate is finished, and it is ready to be mounted on the boat. The holes need to be drilled and the plate mounted. We will use 3M Marine 5200 to bond and seal the transom plate to the boat transom. Once the transom plate is in place, we will seal the nuts and bolts with 3m 4200 Fast Cure.

Drilling holes in Jon Boat Transom

So the plate is ready to be mounted to the boat transom. I measured the center of the transom and kept an eye out for rivets. Once I had the plate where I wanted it, I clamped it in place. Using the plate as a template, I drilled the holes in the transom starting from the bottom. I drilled the the two bottom holes first, put the bolts and nuts in place, and then tightened them down. Then I moved to the center holes, and then to the top holes. With the plate in place, I taped around the plate so the 3M 5200 wouldn’t leak onto anything that I cared about. I also taped the plate too so I would have nice lines when I finished applying the 5200.

Once all the holes were drilled, I removed the plate from the transom, and got ready to forever bond the plate to the transom. I prepped both mounting surfaces by sanding them down and wiping them with acetone. Once cleaned, they were ready for the 3M Marine 5200.

3M Marine 5200

To forever bond this plate to the transom, I used 3M 5200. 3M 5200 is a permanent bond. It is very hard to remove anything that had 3M 5200 on it. You either have to use a wire, or remove material to take an object away from the 3M 5200’s grasp. So it will work great for this plate to transom mount.

All the mating surfaces are prepped and we are ready to get this 3M 5200 onto them. I used the regular cure stuff which takes 7 days to fully cure, and maybe even longer in my case. 3M offers a 5200 Fast Cure which cures in a day or two if you don’t have that kind of time. I would have liked the fast cure but I did not know about it.

So I applied a generous amount to the plate; slapped it onto the transom; put the bolts, washers, and nuts in place and tightened them down; and then applied the clamp in the middle to help get even pressure on the plate.

One Week Later

The plate stayed bolted and clamped on the transom for 8 full days. I did not seal the the bolts, nuts, and washers yet, but that’s where the 3M 4200 Fast Cure comes in. I didn’t seal the bolts with the 3M 5200, because I wanted to be able to get them out if needed. 3M 4200 isn’t permanent, but its not easily removable so that is what we will use on the bolts to seal them. 3M 4200 Fast Cure is good to use under the waterline.

Now to seal each bolt! I did seal the bolts one at a time. I would take the bolt out; put a bead of 4200 on the back side of both washers, a little dab in front of the nut, and by the head of the bolt; put the bolt back in and tighten it up. I did that six times (every bolt was done) and now the transom is reinforced, and water tight!

3M 5200 vs 3M 4200 Fast Cure

So you may be wondering when to use 5200 or to use 4200. Think of 3M 5200 as permanent. You can remove it with special products, but most of the time you will damage whatever you try taking it off of because it is so strong. 3M 4200 or the 3M 4200 Fast Cure is not easy to remove, but its less permanent than 5200.

3M 5200 – Permanent. You have no need to remove that object for a long time.

3m 4200 Fast Cure – You need that object to stay there, but you may need to remove it one day.

Both are good for under the water line. They both seal and the 5200 come in a regular cure or a fast cure, and the 4200 only comes in a fast cure. 3M 4200 is NOT the same as 3M 4000!

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